The present invention relates to using electromagnetic fields and in particular radio frequency electric and magnetic fields to crack or upgrade heavy hydrocarbons. Upgrading heavy hydrocarbons aids in the extraction and processing of hydrocarbons into valuable fuels. In particular, the present invention relates to an advantageous radio frequency (RF) applicator and method that can be used to crack heavy hydrocarbons. The invention breaks the usually unreactive carbon-carbon (C—C) bonds of aromatic molecules, which can be used to upgrade bitumen, reduce the aromatic content of gasoline, or assist in petrochemical synthesis.
As the world's standard crude oil reserves are depleted, and the continued demand for oil causes oil prices to rise, oil producers are attempting to process hydrocarbons from bituminous ore, oil sands, tar sands, oil shale, and heavy oil deposits. These materials are often found in naturally occurring mixtures of sand or clay. Because of the extremely high viscosity of bituminous ore, oil sands, oil shale, tar sands, and heavy oil (heavy hydrocarbons for short), the drilling and refinement methods used in extracting standard crude oil are typically not available. Enhanced oil recovery (EOR) processes are required.
Current EOR technology heats the hydrocarbon formations through the use of steam and sometimes through the use of RF energy to heat or preheat the formation. Steam has been used to provide heat in-situ, such as through a steam assisted gravity drainage (SAGD) system. Steam enhanced oil recovery may not be suitable for permafrost regions due to surface melting, in stratified and thin pay reservoirs with rock layers, and where there is insufficient caprock. At well start up, for example, the initiation of the steam convection may be slow and unreliable as conducted heating in hydrocarbon ores is slow. Water resources may be insufficient to make steam.
RF heating methods use connate in situ water, such as pore water, which is generally present in a hydrocarbon formation. Water is easily heated by electromagnetic fields, so an underground antenna can heat hydrocarbon formations. The electromagnetically heated pore water conductively heats the hydrocarbons. Because electric and magnetic fields travel near the speed of light, RF heating provides greatly increased speed and penetration through conduction and convection. RF energy can also penetrate impermeable rocks to heat beyond. A radio frequency electromagnetic means to crack and upgrade oil in situ is valuable, especially if accompanied by well stimulation.
Heavy hydrocarbons, such as crude oil and bitumen, often contain aromatic molecules, which make the oil thick and heavy, and thus difficult to extract. Aromatic molecules are molecules, such as benzene, where the atoms are joined together in a ring shape. Breaking the aromatic rings, which is also known as cracking, creates lighter and thus easier to extract polar hydrocarbon molecules. This process is known as “upgrading” the oil. Aromatic molecules are exceptionally stable molecules and are therefore very difficult to crack. Thus, using radio frequency magnetic fields to crack aromatic molecules can be advantageous.
RF electromagnetic (EM) fields can interact strongly with some molecules and weakly with others. In a mixture of molecules, RF EM heating can increase the kinetic energy of one type of molecule without increasing the kinetic energy of other molecule types, which results in selective heating. Thus, high localized temperatures can be achieved without excessively heating a material in bulk. Temperature plays an important role in determining the rate and extent to which chemical reactions occur. Thus, RF EM fields can be effective to cause reactions involving hydrocarbon molecules.
Gasoline is the ubiquitous fuel for automotive transportation. The United States used 140 billion gallons in 2005. In order to meet this demand, modern gasoline is a blend of hydrocarbon molecules typically ranging from 4 to 12 carbons (C4 to C12). Many types of gasoline molecules, such as aromatic molecules, are hazardous substances that are regulated in the United States and elsewhere. While aromatic molecules are beneficial for high octane (benzene has an octane value of 101), they are released in engine exhaust and evaporated when the gas is pumped. Thus, gasoline formulation includes tradeoffs in choosing the hydrocarbon molecular species, the emissions level, and the toxicity level of those emissions.
Benzene has been identified as a toxic air pollutant and a potent carcinogen in the US Clean Air Act of 1990. Measured amounts of benzene in polluted city atmospheres are known to cause leukemia, lung, and skin cancer. In view of such severe health effects, the United States Environmental Protection Agency enacted regulations that will lower the benzene content in gasoline to 0.62% in 2011 (“Control of Hazardous Air Pollutants From Mobile Sources”, U.S. Environmental Protection Agency, 2006 Mar. 29. p. 15853 (http://www.epa.gov/EPA-AIR/2006/March/Day-29/a2315b.htm)). Removing aromatics from gasoline reduces toxic emissions which in turn reduces the incidence of leukemia and other cancers. Technologies to reduce benzene levels are needed.
Modern gasoline is a product of varying refinery processes. The Fluid Catalytic Cracking Unit (FCCU) is an example of a process that breaks large high boiling range hydrocarbons into gasoline range products. FCCU output may contain 30 percent aromatics. In a typical FCCU, aromatics like benzene may undergo little cracking. Catalytic Naptha Reforming Units (CNRU) convert saturated low octane hydrocarbons into higher octane products containing 60 percent or more aromatics. Therefore, in a CNRU toxic aromatics are in fact created, especially so if C6 is included in the feedstock. Methods to adjust FCCU and CNRU output aromatic levels can be advantageous.
Steam cracking is a process in which heavier hydrocarbons are mixed with water and heated to high temperatures such as 900° C. to break down heavier hydrocarbons into smaller, lighter hydrocarbons. In steam cracking radical addition may occur to form new aromatic molecules, yet it may be desired to not form aromatic molecules. A steam cracking process that does not produce aromatics can be advantageous.
U.S. Pat. No. 6,303,021 to Winter et. al, and entitled “Apparatus and Process For Improved Aromatic Extraction From Gasoline” describes a glycol solvent based process for separating gasoline aromatics that includes contacting the feedstock with solvent vapors. Means to actually crack the aromatic molecules are not provided.
A list of possibly relevant patents and literature follows:
4,645,585White6,303,021Winter6,106,895Usuki4,404,123Chu3,991,091Driscoll et alDielectrics and WavesArthur H. Von Hippel(John Wiley and Sons) p. 154